hwc: Set GPU performance hint.

1. Set the GPU hint flag to high for MIXED/GPU composition only for
   first frame after MDP to GPU/MIXED mode transition.
2. Set the GPU hint to default if the current composition type is GPU
   due to idle fallback or MDP composition.

Change-Id: I208a778017435a5a4620142da9d9fb3c50e09155
diff --git a/libhwcomposer/hwc_mdpcomp.h b/libhwcomposer/hwc_mdpcomp.h
index 22b8baf..2d65755 100644
--- a/libhwcomposer/hwc_mdpcomp.h
+++ b/libhwcomposer/hwc_mdpcomp.h
@@ -53,6 +53,7 @@
     static bool init(hwc_context_t *ctx);
     static void resetIdleFallBack() { sIdleFallBack = false; }
     static void reset() { sHandleTimeout = false; };
+    static bool isIdleFallback() { return sIdleFallBack; }
 
 protected:
     enum { MAX_SEC_LAYERS = 1 }; //TODO add property support